Field of the Invention

The present invention relates to a modular scaffolding system, and more in particular, to a modular scaffolding system for supporting formwork.

Background

Modular scaffolding systems comprise a limited number of different building elements that can be connected together in large numbers to form a variety of scaffold frames. Due to their modular nature, the scaffold frames may be individually tailored to specific sites and applications. The propping of loads, e.g. formwork, during construction works is an example of such an application.

In general terms, a modular scaffold frame set up to prop a load typically comprises a plurality of standards (also called uprights), ledgers and cross-braces. The standards are connected to form vertically extending columns that are spaced apart at regular intervals. Horizontally oriented ledgers interconnect the columns at different height levels to form a more or less regular framework. Points where ledgers connect to standards are called nodes. The cross-braces may diagonally interconnect these nodes, either connecting nodes of the same level or connecting nodes of different levels, in order to increase the rigidity of the scaffold frame. Upper standards of the columns may further be provided with forkheads, which provide a support for girders or support beams that may in turn support the actual load.

The heights of the load-bearing forkheads of the scaffold frame need to be aligned with the height-profile of the structure to be supported. Since standards of a modular scaffolding system typically all have the same unit length (e.g. around 500 mm), it is likely that the desired heights of the forkheads are not an exact multiple of the unit length. This issue is normally dealt with by providing the forkheads not on top of fixed-length standards, but on so-called screwjacks, i.e. standards whose effective length can be adjusted. The screwjacks are preferably configured such that their length can be adjusted continuously over a distance of about one standard unit length. Accordingly, the desired height of a forkhead mounted on such a screwjack is also continuously adjustable. A problem may arise when a load is applied to a forkhead mounted on an extended screwjack. Under certain conditions (e.g. side winds acting on a propped load) the forkheads may be subjected to non- vertical forces, which in turn may give rise to considerable bending stresses in the extended screwjacks that support them. The greater the degree of extension of a screwjack, the greater the experienced bending stress for the same non-vertical force. The bending stresses diminish the supporting capability of the screwjacks, and hence of the entire scaffold frame, and are therefore best avoided.

Two solutions to this problem have been put forward. The first solution entails the extension of the screwjacks to a lesser degree, and the additional use of base jacks (i.e. jacks that support the columns of a scaffold frame from below) to set the heights of the forkheads. The total required extension is thus divided between the base jacks and the screwjacks, such that neither of them needs to be fully extended. A drawback of this first solution, however, is that it is practically impossible to adjust the degree of extension of a base jack once a scaffold frame has been put up. Indeed, this is because the entire weight of the frame rests on the base jacks. A second, alternative solution is shoring up the individual screwjacks to a lower ledger level of the scaffold frame. Unfortunately, individually shoring up the screwjacks is a toilsome job, and what is more, it is prone to an asystematic approach that may lead to errors endangering the stability of the scaffold frame. It is an therefore an object of the present invention to overcome or mitigate one or more of the above-mentioned problems associated with the use of extendable screwjacks. Summary of the Invention

According to one aspect of the invention, a forkhead for use in a modular scaffolding system is provided. The forkhead comprises an axially extending shaft having a first end and a second end, and a fork structure that is connected to the first end of the shaft. The forkhead also comprises coupling means, provided on the shaft and configured to rigidly connect an end of at least one ledger to the shaft in an axial ledger connection range. The forkhead further comprises a mounting assembly configured to pivotally mount the forkhead to a standard.

The forkhead according to the invention is formed as a separate modular component that is detachably connectable to a standard, such as a screwjack, upon use. It connects to the standard in a pivotal manner, which advantageously diminishes torsion en bending stresses in the forkhead shaft and the standard, especially compared to a rigid connection between the two components. The forkhead features integrated coupling means that enable the use of its elongate, axially extending shaft in a manner analogous to the use of a common standard. In use, the shafts of different forkheads may thus be interconnected by a level of ledgers. It is understood that each connection between a ledger and a forkhead shaft may preferably be rigid (Dutch: "stijf ', "star" or "momentvast") in nature, so as to enable the formation of a (top) level of ledgers that rigidly interconnects the forkheads. This (top) level may then, as a whole, be shored to a lower level of ledgers of the scaffold frame, which lower level may be shored to a still lower level, and so on to ground level. Doing so ensures that non-vertical forces on the forkheads are taken up by the top level of ledgers and diverted downwards from there, effectively bypassing the standards that support the forkheads. This reduces exposure of the standards to the non-vertical forces, and thus to detrimental bending stresses that could result therefrom. Because the top level of ledgers that interconnects the forkheads is shored to a lower level of ledgers in its entirety, only a limited number of shores is required. A shore to forkhead ratio of 1:5 or less (e.g. 1:10 or 1:15) will typically suffice, which means that the work involved in raising a secured scaffold frame for propping a load is greatly reduced, in particular in comparison to individually shoring the forkhead carrying standards.

Ledgers may be connected to the shaft in an 'axial ledger connection range'. This range is defined by the axial or longitudinal portion of the shaft over which a connected ledger is in contact with the shaft. According to an embodiment of the invention, the axial ledger connection range extends within a distance of 0 to 25 cm from the first end of the shaft.

To expose as little of the shafts of the forkheads and the standards that support them to non-vertical forces (and hence bending stresses), ledgers preferably connect to the forkhead shafts just below their load-bearing fork structures. To this end, the coupling means are preferably disposed within a distance of about 25 cm from the first end of the shaft of the forkhead, or at least configured to connect a ledger to the shaft within said range of 0 to 25 cm from the first end.

According to another embodiment of the present invention the mounting assembly comprises the second end of the shaft, said second end being open and configured to receive an end portion of a standard. The mounting assembly further comprises an internal stop surface, disposed in the shaft and configured for cooperation with a stop surface on the end portion of the standard.

To provide for a pivotal connection with a standard, the forkhead may be provided with a female mounting provision in the form of an open ended shaft that is capable of receiving a male mounting provision in the form of an end portion of a standard. The open end of the shaft effectively serves as a socket that has an internal stop surface against which, in use, a stop surface on the end portion of the standard may abut so as to transfer any vertical load from the forkhead onto the standard. The female-male

connection thereby reliably secures the two components relative to each other.

According to a further embodiment of the present invention, an axial position of the internal stop surface is within the axial ledger connection range.

Due to the preferably slightly pivotal connection between the forkhead and a standard, the shaft of the forkhead and the standard need not be in complete alignment with each other. While the standard is typically oriented vertically, the shaft of the forkhead may extend in a slightly non- vertical direction. Ledgers typically connect to the shaft in a direction perpendicular thereto. This configuration implies that (even) substantially vertical load forces on the fork head include both force components acting in the direction of the shaft of the forkhead, and force components acting in a direction parallel to the ledgers. The latter force components may be partly absorbed by the ledgers, and also partly by the standard. The fact that the standard may experience the effects of force components parallel to the ledgers is because said force components— acting on the fork structure of the forkhead— generate a moment relative to points in the axial ledger

connection range. In case the end portion of the standard does not coincide with the axial ledger connection range, an arm exists between the end portion of the standard and the axial ledger connection range through which the end portion of the standard may be forced to balance the moment generated by the aforementioned force components. Consequently, the end portion of the standard that supports the forkhead may be forced in a non-vertical direction, which again leads to a bending moment. This is clearly undesirable. To minimize such bending moments, the internal stop surface of the forkhead may preferably be disposed within the axial ledger connection range, and more preferably near the axial center thereof (e.g. no further than 10% of the axial length of the axial ledger connection range from an axial center of the axial ledger connection range). Such placement effectively eliminates the arm that might otherwise exist between the connection of the standard with the shaft on the one hand, and the connection of the shaft and the ledgers on the other, forcing this latter connection (which is capable of supporting a force couple) to balance moments generated by the force components that do not extend parallel to the shaft.

With the internal stop surface of the shaft in the axial ledger connection range, load forces on the fork structure of the forkhead may be said to travel down the shaft, and split up at or around the axial position of the internal stop surface. Substantially vertical forces pass through the pivot formed by the two abutting stop surfaces of the forkhead and the standard, while substantially non-vertical forces are led into the at least one ledger that connects to the shaft at that position. As mentioned, said at least one ledger is to form part of a (top) level of ledgers that is shored to a lower level of ledgers, and so on, in order to safely guide any non- vertical forces experienced by the forkheads downwards through the scaffold frame. No moment due to substantially horizontal forces or force components is transferred onto the standard as the pivot formed by the two abutting stop surfaces lies within the axial ledger connection range. The result of this configuration is therefore that the standard merely experience a substantially vertical compressive load, and virtually no bending moment that may compromise its supporting capability.

According to a further elaboration of the invention, the internal stop surface of the forkhead is spheroidally curved.

A connection between the forkhead and a standard via their two aforementioned stop surfaces allows for some play. The shaft of the forkhead may, for example, be allowed to rotate a few degrees out of alignment with the standard. To enable smooth mutual reorientations of the forkhead and the standard under a varying load, and to minimize wear of the stop surfaces, the internal stop surface of the forkhead is preferably spheroidally curved. The stop surface on the end portion of an associated standard is, of course, preferably shaped complementarily to enjoy the full benefits of the

configuration. Thus, in case the internal stop surface is curved concavely, the stop surface of the associated standard is preferably shaped convexly, or vice versa.

Another aspect of the present invention is directed to a method of constructing a scaffold frame. The method comprises providing a plurality of standards, ledgers and couplers, and constructing a scaffold frame therefrom, wherein the standards form a plurality of vertically extending columns that, through the intermediation of the couplers, are interconnected by the ledgers at different height levels. The method also comprises providing a plurality of forkheads according to the present invention, and operably mounting the forkheads on the standards disposed at/forming the upper ends of the colums. These latter standards may typically be length-adjustable standards, such as screwjacks. An upper standard may, for example, comprise an inner tube, an outer tube, and an adjusting nut, wherein the inner tube and the outer tube are telescopically arranged relative to each other; wherein the inner tube is, over at least a part of its length, provided with an external thread; and wherein the adjusting nut is provided on the threaded part of the inner tube, such that the standard forms a screwjack. The inner tube may have an end portion that is receivable by the second end of the shaft of the forkhead, said end portion having a frontal stop surface that is configured for pivotal contact with the internal stop surface of the forkhead. The method includes rigidly interconnecting the forkheads by means of their coupling means and a plurality of ledgers, so as to form a substantially rigid top level of ledgers, and shoring said top level of ledgers to a lower level of ledgers at a number of shoring positions, whereby the shore to forkhead ratio (i.e. the ratio of the number of shoring positions to the number of forkheads) is 1:5 or smaller. The forkhead's integrated coupling means enable and facilitate the use of its elongate, axially extending shaft in a manner analogous to the use of a common standard. In use, the shafts of different forkheads may thus be interconnected by a rigid level of ledgers. This (top) level may then, as a whole, be shored to a lower level of ledgers of the scaffold frame, which lower level may be shored to a still lower level, and so on to ground level. Doing so ensures that non- vertical forces on the forkheads are taken up by the top level of ledgers and diverted downwards from there, effectively bypassing the standards that support the forkheads. This reduces exposure of the standards to the non-vertical forces, and thus to detrimental bending stresses that could result therefrom. Because the top level of ledgers that interconnects the forkheads is shored to a lower level of ledgers in its entirety, only a limited number of shores is required. A shore to forkhead ratio of 1:5 or less (e.g. 1:10 or 1:15) will typically suffice, which means that the work involved in raising a secured scaffold frame for propping a load is greatly reduced, in particular in comparison to individually shoring the forkhead carrying standards.

These and other features and advantages of the invention will be more fully understood from the following detailed description of certain embodiments of the invention, taken together with the accompanying drawings, which are meant to illustrate and not to limit the invention.

Brief Description of the Drawings

Fig. 1 is a schematic perspective view of a known screwjack having an integrated fork structure;

Figs. 2-4 schematically illustrate an exemplary embodiment of a forkhead according to the present invention, whereby Fig. 2 is an orthogonal front view of the forkhead, Fig. 3 is an orthogonal side view of the forkhead, and Fig. 4 is a cross-sectional view of a shaft insert of the forkhead;

Fig. 5 is a schematic side view of a screwjack for use with the forkhead shown in Figs. 2-4; Fig. 6 schematically illustrates a scaffold frame supporting a load; Fig. 7 shows a detail of an upper portion of the scaffold frame shown in Fig. 6, illustrating the configuration of a top level of ledgers connected to the forkheads, whereby said top level is shored to a lower level of ledgers;

Fig. 8 schematically illustrates in a close-up taken from Fig. 7 a connection between a forkhead, a number of ledgers, and a screwjack; and

Figs. 9 and 10 schematically illustrate the working of the coupling means shown in, inter alia, Figs. 2 and 3.

Detailed Description

Fig. 1 is a schematic perspective view of an exemplary known screwjack 1. The screwjack 1 comprises a cylinder jacket- shaped inner tube 2 that is slidingly moveable into and out of a cylinder jacket-shaped outer tube 14. An upper end of the inner tube 2 is fixedly connected to a fork structure 6, for example through a weld. The fork structure 6 includes a substantially rectangular base plate 8, on the corners of which teeth 10 in the form of upstanding angle profiles are mounted. The angle profiles may comprise a number of holes 11. The inner tube 2 is further provided with an outer thread 4 over at least a significant portion of its length. An adjusting nut 12 that is screwable up and down the thread 4 is provided on the inner tube 2.

In use, a girder (not shown) may be supported on the base plate 8 of the fork structure 6, in between the teeth 10. The angular profile of the teeth 10 thereby helps to keep the girder in position. A wooden girder may, if desired, be bolted to the teeth 10 through the holes 11 to prevent it from slipping away. The weight of the girder and that of any load it carries are transferred from the fork structure 6 to the inner tube 2, and via the adjusting nut 12 provided thereon onto an edge or collar 16 of the outer tube 14. It will be clear that, in use, the adjusting nut 12 rests on the edge 16 of the outer tube 14. It is merely for reasons of clarity that the inner tube 2 and the adjusting nut 12 attached thereto are shown in a lifted position in Fig. 1, in particular to make the edge 16 of outer tube 14 visible. As the adjusting nut 12 rests on the edge 16, the height of the fork structure 6 relative to said edge 16 may be adjusted continuously by turning the adjusting nut. Such adjustment of the height of the fork structure 6 is, of course, preferably done before loading it. A lower end (not shown) of the outer tube 14 typically connects the screwjack 1 to the rest of a scaffold frame, which holds this lower end in place.

The screwjack 1 shown in Fig. 1 embodies several drawbacks. The fork structure 6, for example, is fixedly connected to the inner tube 2.

Consequently, non- vertical or slightly off-center vertical loads, i.e. vertical loads on the base plate 8 of the fork structure 6 that are asymmetrically distributed relative to the (axis of the) inner tube 2 that supports it, may expose the join between the base plate 8 and the inner tube 2 to shear strains and bending moments. In addition, an increasingly extended screwjack 1 gives rise to a larger distance (read: arm) between the load-bearing fork structure 6 and the (fixed) lower end of outer tube 14, and hence to larger bending moments in the inner tube 2 under the same non-vertical load. The bending moments induce tensile and compressive stresses in the inner tube 2, and may eventually cause its failure. These drawbacks associated with the known screwjack 1 can be overcome through the use of the forkhead 100 according to the present invention, to which attention is now invited.

Figs. 2-4 schematically illustrate an exemplary embodiment of a forkhead 100 according to the present invention. Fig. 2 depicts the forkhead 100 in a frontal view, Fig. 3 depicts the forkhead 100 in a side view, and Fig. 4 is a cross-sectional view of a shaft insert 140. The construction of the forkhead 100 will now be elucidated with reference to these figures.

The forkhead 100 comprises a shaft 102, having a first end 104 and a second end 106. Since the forkhead 100 may typically be used in a

substantially upright orientation, as shown in Figs. 2 and 3, the first end 104 and second end 106 of the shaft 102 may occasionally be referred to as the upper and lower end of the shaft, respectively. Other relative designations, such as 'above', 'below', etc. may additionally be used to describe other elements as well, and it is understood that such designations derive from the normal orientation of use of the forkhead 100.

Connected to the first, upper end 104 of the shaft 102 is a fork structure 110, similar to the one shown in Fig. 1. It includes a base plate 114 that is joined to the upper end 104 of the shaft 102, e.g. through a weld. The base plate 114 is provided with a number of teeth 112 that are formed by upright angle profiles between which a formwork supporting girder (not shown) may be received. The base plate 114 then supports the girder from below, while the teeth 112 prevent the girder from moving laterally. It will be appreciated that many fork structure designs may be suited to practice the present invention. The number of teeth 112 of the fork structure 110, for example, is primarily a matter of choice, although fork structures with two (i.e. a U-fork) or four regularly arranged teeth (as shown) are most common. The teeth 112 may further have a variety of shapes (e.g. cylindrical, or angular as shown), and the fork structure 110 as a whole may be made of one piece or be assembled from different elements that have been connected together. In principle, any fork structure capable of securely supporting a girder or other formwork (supporting) element is usable.

The shaft 102, which extends substantially perpendicularly from the base plate 114 of the fork structure 110, essentially comprises a hollow, cylinder jacket-shaped tube 108 in which a shaft insert 140 has been inserted during construction of the forkhead 100. The shaft insert 140 - for the sake of clarity shown separately in Fig. 4 - includes a hollow, cylinder jacket- shaped tube 142, a natural outer diameter of which is slightly larger than a natural inner diameter of tube 108, such that the insert may be securely fixed inside tube 108 by means of pressing. When the shaft insert 140 is properly introduced into tube 108, a first end 144 of the shaft insert tube 142 abuts the lower side of base plate 114 of the fork structure 110. A second end 146 of the shaft insert tube 142 is provided with a head 148, a lower surface of which provides a stop surface 150. The stop surface 150 is configured for cooperation with an end portion 166 of a screwjack 160 (to be discussed in relation to Fig. 5 below), with which it forms a hinge point (cf. Fig. 8). To this end, the stop surface 150 is spheroidally curved in such a way that the head 148 defines a concave socket in which a complementarily- shaped stop surface 170 of said end portion 166 of said standard 160 is pivotally receivable. The head 148 may further include a passage 152 to enable galvanization of the tube 142 of the shaft insert 40 once it has been inserted into the shaft's main tube 108.

Although the proposed construction of the shaft 102 is relatively light-weight due to the use of hollow tube segments 108, 140, yet sufficiently strong and economically manufacturable, it is contemplated that the shaft of the forkhead 100 may be constructed differently in other embodiments. The shaft 102 may, for example, not have a circular cross-profile (even though this would probably inhibit the interchangeability of these components with components of other modular scaffolding systems), not include a separate shaft insert 140 (the internal support surface 150 may for example be formed by a portion of the base plate 14 of the fork structure 10), or possibly, not even have an internal support surface 150 (it is conceivable that the second end 106 of shaft 102 is to be received in a socket provided in a supporting standard, instead of the other way around as shown in Figs. 2-4). Such embodiments are all intended to fall within the scope of the present invention.

The shaft 102 is provided with coupling means 120 to enable one or more ledgers to be linked to the shaft. The coupling means 120 include a first, upper cup 122; a second, lower cup 132, and a cam 130. The second, lower cup 132 is rigidly connected to the shaft 102, and it defines an annular cup space 134 between an outer circumference of the shaft 102 and an inner

circumference of an upwardly extending wall 133 of the cup. The first, upper cup 122 is not rigidly fixed to the shaft 102, but instead slidingly moveable along it, namely in between the base plate 114 of the fork structure 110 and the second, lower cup 132. Like the lower cup 132, the upper cup 122 defines an annular cup space 124, this time between an outer circumference of the shaft 102 and an inner circumference of a downwardly extending wall 123 of the cup. The first, upper cup 122 further includes a helically sloping brim 128 (of only one turn). The sloping brim 128 is configured for cooperation with the cam 130, which is provided on an outer circumference of the shaft 102.

It is noted that the above- described configuration of the coupling means 120, wherein the lower cup 132 and the cam 130 are fixed to the shaft 102, and the upper cup 122 is trapped on the shaft, in between the lower cup and the base plate 114, prevents any part of the coupling means 120 from getting lost or accidentally falling down when working at an altitude.

Figs. 9 and 10 illustrate how the coupling means 120 may be used to join ledgers 180 to the shaft 102. In Fig. 9, the upper cup 122 is suspended on the cam 130. This allows one to place a number of ledgers 180, each having a flange 182 on both ends, in the lower cup 132. When all ledgers 180 are positioned (typically no more than four), the upper cup 122 may be lowered by sliding the cam 130 through the slot 126 so as to lock up the upper parts of the flanges 182 in the cup space 124. See Fig. 10. Subsequently turning the upper cup 122 clockwise brings the sloping brim 128 in wedging contact with the cam 130. Tightening the upper cup 122 by turning it further clockwise rigidly clamps the flanges 182 of the ledgers 180 between the cups 122, 132, and against the shaft 102 in the axial ledger connection range 109. Releasing the ledgers 180 is, of course, done by executing the steps in opposite order. The proposed coupling means 120 enable one to safely yet quickly interconnect the forkheads 100 by means of ledgers 180, which is an improvement over the situation wherein individual forkhead carrying standards must be shored using conventional, somewhat awkward (and often separately provided) couplers. It is understood that the forkhead 100 according to the present invention may be fitted with different coupling means than those described with reference to Figs. 2-4. In an alternative embodiment, for example, the shaft 102 of a forkhead 100 may be provided with a generally disc-shaped, annular rosette that is fixedly connected, e.g. welded, thereto. The rosette may comprise a number of preferably angular openings that may be spaced along the circumferential direction of the rosette. Ledger ends may then be fitted with a recess in which a part of the rosette is receivable, and with a wedge configured to be driven through an opening provided in the received part of the rosette so as to rigidly lock the ledger to the forkhead 100.

More generally, coupling means provided on the forkhead shaft 102 of a forkhead 100 according to the present invention may preferably be configured to rigidly connect or facilitate the rigid connection of a ledger end to the shaft 102. The fact that the coupling means are provided on the shaft 102 of the forkhead 100 (e.g. permanently/irremovably, yet possibly movably connected thereto (cf. upper cup 122 described above)) may facilitate use of the forkhead 100 as it need not itself be assembled prior to use, and may enable rigid connections resistant to rotational motion of a connected ledger relative to/around the typically cylindrically shaped shaft 102 of the forkhead 100. Indeed, clamps provided on ledgers ends that are configured to clamp such a cylindrical shaft 102— as sometimes seen in the prior art— are often prone to allow for turning of a respective ledger relative to the clamped forkhead shaft 102, which may be undesirable.

Fig. 5 schematically illustrates a screwjack 160 on which the forkhead 100 shown in Figs. 2-4 is mountable. The screwjack 160 comprises two cylinder jacket-shaped tubes 162, 172, one of which 162 is receivable in the other 172 in a telescoping manner. Inner tube 162 is, over an upper portion, provided with an external thread 164. The screwjack 160 further includes an adjusting nut 168, which can be screwed up and down the threaded portion of tube 162. In use, the adjusting nut rests on an edge or collar 174 of the outer tube 172 by which the part of the tube 162 that extends below the adjusting nut 168 is received. Turning the adjusting nut 168 one way will gradually raise the inner tube 162 from the outer tube 172, while turning it the other way will sink the inner tube 162 into the outer tube 172. Accordingly, the screwjack 160 serves as a mechanism that may be used to raise and lower a forkhead 100, mounted on an upper end portion 166 of the inner tube 162, to the desired height.— It is understood that the outer tube 172 is typically relatively short, i.e. shorter than the unit length of the standards of a modular scaffolding system, and therefore not capable of accommodating the entire inner tube 162 . However, since the outer tube 172 is normally placed on top of other standard-length standards to form a

(hollow) vertical column (193, see Fig.6), the inner tube 162 may in practice slide through the outer tube 172 and into these lower standards, so as to effect a lower forkhead height. - In order to enable a slightly hingeable connection with the forkhead 100, the upper end portion 166 of the inner tube 162 is provided with a spheroidally shaped stop surface 170 that is configured for cooperation with the stop surface 150 of the shaft insert 140. During construction, the stop surface 170 may for example be punched from a metal plate, and then be welded on top of the tube 162.

Fig. 6 schematically illustrates a scaffold frame 190 that is used for propping a load 200, e.g. a layer of formwork. For reasons of clarity, some conventional elements that might in practice be part of the scaffold frame 190, such as, for example, transoms, guardrail ledgers, toeboards etc., are omitted from the drawing. The depicted framework 190 comprises a plurality of standards 192, ledgers 180, couplers 120 and shores 194. The standards 192 are ordinary standards, different from the one shown in Fig. 5 in that they do not include a jack mechanism. In a vertical direction, the standards 192 are connected through conventional spigot-socket fittings (not visible, but each time located near the couplers 120) to form columns 193. These columns 193 are oriented vertically, in parallel and spaced apart at regular intervals. Near ground level, the standards 192 rest on base jacks 196 that allow for adjustment to terrain irregularities. The vertical standards 192 are laced together by horizontally oriented ledgers 180. The ledgers 180 are provided at discrete vertical levels that are spaced apart at regular intervals. In the framework of Fig. 6, the spacing between the levels is three standards 192. The ledgers 180 (preferably rigidly) interconnect the standards 192, whereby the ledgers themselves are linked to the standards through couplers 120 that may be (but need not be) similar to the coupling means provided on the shaft 102 of the forkhead 100 discussed above. Points where ledgers 180 connect to standards 192 are called nodes. Shores 194 may diagonally interconnect these nodes, either connecting nodes of the same level (not visible in Fig. 6) or connecting nodes of adjacent levels, in order to increase the rigidity of the scaffold frame 190.

As can be seen clearly, the load 200 supported by the scaffold frame 190 does not extend in a completely horizontal plane, but at an angle to the horizontal instead. To accommodate to the slope of the load 200, screwjacks 160— where necessary supplemented by a conventional standard 192 (see the left columns)— bridge the distance between the highest truly horizontal level 198 of ledgers 180 and the forkheads 100 that support the load 200. This is best seen in Fig. 7, which illustrates a detail A from Fig. 6. In addition, a top level 199 of ledgers interconnects the forkheads 100, closely below the load- bearing fork structures 110 thereof. This top level 199 - which forms a substantially rigid plane by virtue of the rigid connections between the forkhead shafts 102 and the ledgers 180 (which rigid connections are in turn facilitated by the integrated coupling means 120 of each forkhead 100) - is shored to lower level 198, and so on, down to the ground level immediately above the base jacks 196. Note that the top level 199 is shored to the lower level 198 as a plane. That is: not every forkhead 100 is individually shored to the lower level 198; only selected forkheads 100 from the plane are shored in order to shore the plane 199 in its entirety. Non- vertical forces experienced by the forkheads 100 are thus prevented from being passed on to the screwjacks 160, in which they could give rise to bending stresses that might weaken the load bearing potential of the framework 190. Instead, any non-vertical forces on the forkheads 100 are safely guided into the top level 199 of ledgers 180, and from there on downwards to the ground via shores 194 and the other levels.

In Fig. 6, the number of depicted shores 194 connecting the top level of ledgers 199 to the level 198 below is four (4), whereas the total number of depicted forkheads 100 is eighteen (18). In practice, of course, the forkheads 100 at the top of the scaffold frame 190 may extend in a two- dimensional plane, comprising several rows of forkheads 100 'behind' the front row visible in Fig. 6. It is not necessary for each row of forkheads 100 to be shored individually. For most practical scaffold frames 190, the shore to forkhead ratio (i.e. the ratio of the number of shores 194 connecting the top level of ledgers 199 and the level 198 below and the number of forkheads 100) may be 1:5 or less, e.g. 1:10 or 1:15.

Fig. 8 is a detail B from Fig. 7, and illustrates a connection between a forkhead 100, an upper end portion 166 of an inner tube 162 of a screwjack 160, and two ledgers 180. The Figure clearly shows how the upper end portion 166 is received in the shaft 102 of the forkhead 100, and how the spheroidally shaped stop surface 170 of the standard 160 abuts the

complementarily-shaped stop surface 150 of the forkhead 100. Visible is also how the cups 122, 132 clamp the ends of the ledgers 180 to the shaft 102 of the forkhead 100, such that the flanges 182 contact an axially extending ledger connection range 109 of the shaft 102. Said axial ledger connection range 109 includes the axial position of the stop surface 150 of the forkhead 100.

Although illustrative embodiments of the present invention have been described above, in part with reference to the accompanying drawings, it is to be understood that the invention is not limited to these embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, it is noted that particular features, structures, or characteristics of one or more embodiments may be combined in any suitable manner to form new, not explicitly described embodiments.

List of elements

1 known screw jack

2 inner tube

4 external thread

6 fork structure

8 base plate of fork structure

10 tooth of fork structure

11 hole in tooth of fork structure

12 adjusting nut

14 outer tube

16 collar or edge of outer tube

100 forkhead

102 shaft

104 first end of shaft

106 second end of shaft

108 cylinder jacket shaped tube

109 axial ledger connection range

110 fork structure

112 tooth of fork structure

114 base of fork structure

120 coupling means / coupler

122 first, upper cup

123 cup wall

124 annular cup space

126 slot for cam

128 sloping brim

130 cam on shaft

132 second, lower cup

133 cup wall of second cup

134 annular cup space of second cup

140 shaft insert

142 tube of shaft insert

144 first end of tube of shaft insert

146 second end of tube of shaft insert

148 head of shaft insert

150 stop surface

152 central hole in head 160 screwjack

162 inner tube

164 external thread

166 upper end portion of inner tube

168 adjusting nut

170 stop surface

172 outer tube

174 edge or collar of outer tube

180 ledger

182 flange on ledger

190 scaffold frame

192 upright or standard

193 column of standards

194 shore

196 base jack

198 second highest level of ledgers

199 highest or top level of ledgers

200 load

A detail

B detail